Semiconducting devices are typically fabricated on dies that include a number of connection pads for connecting the circuitry contained on the die to external circuitry. A die is normally packaged in an encapsulating material to protect the die and to provide connections between the pads on the die and connectors that are better adapted for making connections to the external circuitry via traces on printed circuit boards and the like.
One class of semiconductor package utilizes a thin metal carrier that is commonly referred to as a “lead frame” to provide the connections between the die and the connectors that mate with external connectors on the printed circuit board. Examples of such packages are taught in U.S. Pat. Nos. 6,400,004 and 6,433,377. In this type of package, the die is typically attached to one portion of the lead frame. Thin gold wires are then connected between each pad on the die and a corresponding internal connector located on the periphery of the lead frame using a wire-bonding process. The lead frame, die, and connecting wires are then encapsulated in a plastic material that protects the die and provides mechanical strength.
While this type of package is economical, it has a number of disadvantages. First, the I/O connections to the die circuitry are located around the periphery of the lead frame. This arrangement limits the number of I/O connections that can be made to the die. As integrated circuits become more complex, this limitation becomes more troublesome.
Second, power and ground connections are typically made through pins that are similar to the I/O pins. The power connections must run from the peripheral connectors of the lead frame to the die via relatively long wires. This limits the current that can be provided to the chip. This can be particularly problematic in high power circuitry.
Third, the amount of heat that can be dissipated by the package is limited. The encapsulating material impedes heat dissipation via the top surface of the package. While the die is attached to a pad in the lead frame pad, the lead frame sits on the printed circuit board. The amount of heat that can be transferred depends on the contact area and heat resistance of that area. In general, the heat leaving via the lead frame pad is impeded by poor thermal connections between the bottom of the package and the printed circuit board.